v2.4.0.6
Summary of significant accounting policies (Details 5) (USD $)
 0 Months Ended 12 Months Ended
May 03, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2012
CCDG
Dec. 31, 2011
CCDG
Dec. 31, 2010
CCDG
Dec. 31, 2009
CCDG
Non-controlling interests                
Percentage of net profits less capital expenditures of the preceding year allocated to non-controlling interest holders         30.00%      
Distributions to non-controlling interest holders   $ 678,000 $ 547,000 $ 398,000        
Initial term of Detroit Operating Agreement         7 years      
Optional extension period of Detroit Operating Agreement         4 years      
Amount of annual fixed distribution per year under Detroit Operating Agreement         121,000 85,000 85,000  
Non-controlling owners capital account amount   $ 823,000 $ 197,000         $ 0
Convertible preferred stock                
Preferred stock issued (in shares)   0 0          
Preferred stock outstanding (in shares)   0 0          
Warrants exercisable into convertible preferred stock                
Preferred stock warrants outstanding (in shares) 25,196              
Issuance of common stock upon exercise and conversion of preferred stock warrants (in shares) 20,172